On average, a typical 4-cylinder vehicle operating at 50 miles per hour will produce approximately 4,000 explosions per minute within its internal combustion engine as the spark plug ignites fuel in each cylinder. If not for the cooling system, the engine would be heavily damaged due to the large amount of heat created.
The cooling system or cooling loop in a vehicle includes, generally, a coolant reservoir for storing coolant (or antifreeze) not currently in circulation, passages within the engine block and heads, a water pump for circulating the coolant through the passages, a thermostat for regulating the flow of the coolant, and a radiator for drawing heat out of the coolant.
The coolant reservoir functions to store excess or overflowing coolant. The coolant reservoir includes a coolant reservoir cap which, when removed, allows for additional coolant to be added into the cooling reservoir and, in turn, pumped through the cooling loop. Standard coolant reservoir caps can withstand a pressure buildup within the reservoir of approximately 21 psi.
As coolant flows out of the coolant reservoir and through the various passages of the cooling loop, it draws heat away from the surrounding components, thereby cooling the engine. Thereafter, the coolant flows through the radiator and is cooled by fresh air entering the engine compartment through the grill in the front of the vehicle. This process repeats as the coolant is recirculated through the engine in order to continually draw heat away from the engine.
Hybrid vehicles include an inverter for converting the direct current output from the battery to alternating current used by an electric motor. This conversion produces additional waste heat that needs to be dissipated. Therefore, hybrid vehicles will oftentimes include a secondary or “inverter” coolant reservoir for specifically cooling the hybrid components in a lower temperature cooling loop, such as an electric motor, a DC-DC power converter, a charger, and the like. The inverter coolant reservoir is separate from the internal combustion engine coolant reservoir.
Coolant, conventionally used in today's internal combustion engine also referred to as antifreeze, is created by mixing water with a suitable organic chemical, such as ethylene glycol, diethylene glycol, or propylene glycol. This mixture allows for the coolant to remain a liquid at very low temperatures (below 0° C.) and avoid evaporating at very high temperatures (above 100° C.). However, as coolant gets hot, it begins to expand and causes an increase in pressure within the cooling system. Therefore, the radiator includes a radiator pressure cap that maintains the pressure in the cooling system by releasing a small amount of coolant through the cap as necessary to equalize the pressure therein. When additional coolant is required for circulation, coolant flows of a respective coolant reservoir.
In order to prevent a buildup of pressure within the coolant reservoir, itself, coolant reservoirs typically include a marking or “max fill line” formed thereon to indicate when the coolant reservoir is filled with an appropriate level of coolant. However, it is not uncommon for people to unintentionally fill the coolant reservoir above the max fill line. As a result, when the coolant stored within the coolant reservoir becomes heated, the expanding coolant causes pressure to build within the reservoir and the cooling loop. This creates an increased risk of the coolant reservoir rupturing or coolant leaking out of the reservoir and damaging the surrounding components.
The prior art addressed this situation by proposing a number of devices to counteract the increased pressure within a cooling system, such as those disclosed in U.S. Pat. Nos. 1,520,212, 2,663,451, 2,840,034, and 3,415,405, and U.S. Patent Application Publication No. 2007/0243463.
In view of the state of the art, it may be advantageous to provide an improved cap for a low temperature cooling loop reservoir in a hybrid vehicle. As in so many areas of vehicle technology, there is always room for improvement related to various vehicular cooling system components.